Floral Splendour and Shortage of Nutrients - Soil: Reflections on the Basis of our Existence - page 52

only graze tender false oat-grass shoots; controlled burning is needed when the
grass gets too thick—a method that also combusts some of the nitrogen content.
Another method is to grow rye and then harvest the crop as a way of removing soil
nutrients.
Jasione and stonecrop are popular sources of pollen and nectar for the many
insects that live at rabbitland—and the combination of a rich flora and sandy soil
makes the area one of the best in Sweden for wild ground-dwelling bees. Forty-
five different species occur here, many of them threatened and in decline both in
Sweden and internationally.
In the middle of the area is a gentle hollow where I often pause on my
nightly strolls. We used to call it the long-jump pit when the children were
small, and we ran up and down setting new records as the kids grew up. The
hollow, dug by local children using buckets and spades in the 1970s, is today
one of the best spots for the ground-dwelling bees that have brought the area
to the attention of entomologists. The loose sand that slides down the sides of
the sandpit creates perfect conditions for the bees. The local authority has cop-
ied the sandpit concept by excavating similar hollows throughout the field to
improve conditions for the bees. Perhaps it is due to the children that bees now
thrive here and large sums of money are being invested to keep encroaching
vegetation at bay.
Nature Can Self-pollute
Local changes in soil chemistry can sometimes cause abrupt changes in the local
flora. Heavy metals occur naturally in some soils, and just as they are toxic to
humans, so they can be harmful to plants in high concentrations, though some spe-
cies have learnt to adapt to such conditions.
Plant mapping is used widely internationally to discover new mineral deposits.
Geotechnical engineers discovered the area in Kastad, Norway, with high concen-
trations of lead in the soil (see previous chapter) by studying changes in the flora
using satellite images. Alpine catchfly has been used to indicate copper deposits
and alpine chickweed to denote the presence of serpentine, a rare mineral created
under special conditions during the formation of mountain ranges by movements
in the Earth's tectonic plates. Serpentine presence results in nutrient-poor soil with
high concentrations of heavy metals such as nickel, chromium and cobalt. Most
plants—apart from alpine catchfly—cannot tolerate such environments. Various
similar examples can be found around the world. In the US state of Oregon, for
example, Douglas fir gives way to pine in areas of serpentine soil as the latter can
tolerate the heavy metals present in the soil.
Serpentine soil is rich in magnesium but low in potassium, which often leads
the plants growing there to suffer from a deficiency. There is usually enough mag-
nesium in most soils, but sometimes the high magnesium content in serpentine soil
can be critical for plant survival. When, in the 1970s and 1980s, spruce forests in